C++ Bark-scale approximation

bark-scale.hpp

	template<typename Sample=double>
	struct BarkScale {
		Sample barkToHz(Sample bark) const {
			return (a + b*bark)/(c + d*bark);
		}
		Sample hzToBark(Sample hz) const {
			return (c*hz - a)/(b - d*hz);
		}
		Sample barkToBw(Sample bark) const {
			Sample div = c + d*bark;
			return bcad/(div*div);
		}
		Sample hzToBw(Sample hz) const {
			Sample l = b - d*hz;
			return l*l/bcad;
		}
	private:
		// specialised from signalsmith::curves::Reciprocal<>::barkScale
		static constexpr Sample a = -289.6141814389989;
		static constexpr Sample b = 1176.757038581856;
		static constexpr Sample c = 15.33854709767119;
		static constexpr Sample d = -0.5528328119568996;
		static constexpr Sample bcad = b*c - a*d;
	};